docs: def get_income_in_period(self, start: datetime, end: datetime) -> Decimal:
          """ Returns all income in the given period """
          accounts = self.get_income_accounts()
          income = Decimal(0)
          for acct in accounts:
              acc_agg = AccountAggregate(self.book, acct)
              acc_bal = acc_agg.get_balance_in_period(start, end)
              income += acc_bal
  
          return income